Mischa Barton Criminally Forgetful on "Law & Order: SVU"?

We admit a certain soft spot for Mischa Barton ever since she went completely nutso and drowned a lovely set of pool furniture as troubled Marissa Cooper on "The O.C."

But in the ensuing years, we've watched with concern as she's been busted for D.U.I., gone to rehab, showed off an alarmingly spindly figure, ended up in a psych ward (ostensibly from a wisdom teeth extraction gone wrong), and had her comeback gig on "The Beautiful Life" end after two episodes.

And it looks like our worries for the beleaguered starlet, 23 (yep, she's really only 23), aren't going to ease up anytime soon.

Reports of trouble have surfaced about her hyped guest-starring stint as a prostitute on "Law & Order: SVU," and not just because the costume department outfitted her in a flea-bitten leopard-print coat, strappy white platforms and thick, non-working-girl-friendly fuchsia tights.

According to Radar Online, Barton repeatedly stumbled over her lines during shooting this week opposite star Mariska Hargitay, resulting in a 10-hour day that yielded only one scene.

"She only had seven lines, seven!" fumes an on-set snitch. "Each time she would mess up, she would forget her lines and Mariska kept prompting her and saying, 'It's your line, Mischa.'"

Every fluffed piece of what was likely typically intense, brow-furrowing "SVU" dialogue apparently elicited a "sorry" from Barton, although it seems that wasn't enough to avoid being hit with the dreaded "unprofessionalism" label from cast and crew.

On the plus side, "She looks pretty," says the spy, and she "always looked happy when she was playing with [her] dog." When the long, line-eluding day finally came to an end, the actress reportedly picked up her pooch and "ran to her trailer."

Meanwhile, could Mischa's alleged on-set problems be the product of a few too many late nights? A source maintains to the New York Daily News that she has been taking a bite out of the Big Apple's club scene.

"She's been 'off' at work, and I'm not surprised, judging from how hard she parties," the spy purports to the paper. "It's scary to think what will happen if she keeps going out like she does."

Barton's rep, however, insists that "everything's going swimmingly," and a staffer on the show tweeted in her defense, "Her footage is great. They are on schedule and her performance is solid. I think the press loves to be mean. It sells, so let's reserve judgment on her. So far, from our end, she is doing great."

Still, the snitch has doubts.

"People close to her were hoping this would get her back on track," the insider tells the Daily News. "But it looks like she's going to need yet another chance."

Just maybe not on the small screen playing a hooker with a lollipop habit.

"I think I need to back away from the whole TV approach," Mischa told People magazine in October. "That whole world of network television, probably isn't, for me, a good idea now. I need to start reading for more serious roles."